Conventionally, an electric compressor is disclosed as an example of a device, in which an electric device is mounted, in the patent document No. 1. The electric compressor includes a housing with a cooling medium suction port and a cooling medium discharge port, a compressing mechanism unit accommodated in the housing, a driving shaft rotatably supported in the housing and transmitting a driving force to the compressing mechanism unit, a stator core accommodated in the housing and arranged on an outer periphery side in a radial direction of the driving shaft, a stator coil accommodated in the housing and winded around the stator core, a rotor arranged on a center side in the radial direction of a rotation axis with respect to the stator core in the housing and rotating the driving shaft according to rotation magnetic field generated by the stator coil, a circuit board (i.e., a driving circuit) as a part of the electric device mounted on an outer wall of the housing and flowing a driving current into the stator coil in order to generate the rotation magnetic field, and a first cooling medium passage disposed between an inner wall of the housing on the circuit board side and the outer wall of the stator core and passing the cooling medium from the cooling medium inlet side to the compressing mechanism side according to cooling medium compression of the compressing mechanism unit.
Since the compressor has the above structure, the electric compressor cools the circuit board via the housing with the cooling medium, which flows through the first cooling medium passage. Further, the first cooling medium passage includes a heat insulating film with respect to the outer wall of the stator core, the heat insulating film preventing heat conduction between the cooling medium and the stator core. Thus, the electric compressor cools the circuit board sufficiently.
However, in the electric compressor disclosed in the patent document No. 1, it is necessary to mount the circuit board on an attachment surface of the outer wall of the housing in order to keep the cooling medium away from the circuit board. Accordingly, the circuit board can mainly radiate heat only from one surface thereof, which contacts the attachment surface of the housing.
To improve the cooling performance of the circuit board, it is considered that the dimensions of the circuit board are increased in order to increase a contact area with the housing. However, when the dimensions of the circuit board are increased, the dimensions of the electric compressor itself are also increased.
Thus, it is considered that the circuit board is arranged in the cooling medium of the housing so that the circuit board is directly cooled by the cooling medium. Conventionally, an electric device is disclosed in the patent document No. 2 as an example of the electric device having the circuit board arranged in the cooling medium of the housing.
In the electric device disclosed in the patent document No. 3, each circuit component (i.e., the circuit board) is electrically connected to a corresponding conduction passage of one conduction passage support (i.e., the circuit board) having flexibility. The circuit component together with the conduction passage support is arranged in a sealed space of the housing (i.e., a casing) under a condition that the flexible conduction passage support is folded. The space of the housing is filled with the non-conductive cooling medium (i.e., coolant). The cooling medium contacts all of the circuit components. Thus, the electric device is structurally compact, and the size of the device is comparatively small. Further, all of the circuit components are homogeneously and sufficiently cooled.    [Patent document No. 1] JP-A-2009-203904    [Patent document No. 2] JP-A-2005-505144
An external coupling terminal (i.e., a connection element) for electrically coupling between the circuit board disposed in the housing and an external circuit disposed on an outside of the housing is hermetically arranged on the wall of the housing in the electric device disclosed in the patent document No. 2. The circuit board and the external coupling terminal are electrically connected to each other in the housing, which is filled with the cooling medium. Thus, the connection portion between the external coupling terminal and the circuit board directly contacts the cooling medium.
When the connection portion and the external coupling terminal directly contact the cooling medium, they may corrode with some kind of cooling medium. Further, for example, when the cooling medium having conductivity is used, the connection portion and the external coupling terminal may be conductive with the cooling medium. Thus, there is possibility to arise problem of reliability when the connection portion and the external coupling terminal directly contact the cooling medium.